It gives a bit relief to find so many Endnote users having the same problem I am having for months. It constantly freezes at start and have to force quite each time (MacOS Sierra). Had tried to rebuild my library twice now but the problem comes back after a while. I have more than 2,000 references in my library. I had doubted that maybe my library is just too large, but from this thread small libraries suffer just the same. Sometimes I become so frustrated that I start to search for alternative software to replace Endnote. It is supposed to improve your productivity and now it has beome a heavy drag. I contacted Tech Support before and they acted like they never knew this is a problem.